An Analysis of the Differences in Prepress Production Software in Screen Printing

Computers have now become an important tool in the screen printing industry. They can help companies reduce many time-consuming preparations, but there are still many difficulties in fully utilizing the functions of computers.

Examples are given to illustrate this issue. A seemingly simple print at the time of arrival may become increasingly tricky over time. For example, a series of small transparent paper back prints are used as product identifiers for electronic devices. The overall design content includes a more complex logo and some text that needs to be printed in two colors on a background color.

The customer gave us a disk and indicated that if there is a problem, the designer can be contacted. When we first looked at these files, we found that all the image elements were created by Photoshop software. The first question is why did they create a file in Photohshop?

Admittedly, Photoshop is a powerful software. Many printers are happy to use it to handle four-color printing. However, it is a bitmap type software. Screen printing production department always encounters a lot of trouble when dealing with the originals generated by bitmap software. Let's take a look at the specific reasons.

Raster and vector

According to the internal principles used by the graphic image processing software to create an image and the types of generated files, they can be divided into two categories: bitmap type and vector type.

When the bitmap software creates an image, it divides the image into easy-to-observe small squares, which are either light or dark depending on the density of the image. As shown below.

The representative software is the drawing software in the Windows operating system. Adobe Photoshop is an advanced bitmap software.

The image composed of bitmaps is obtained after rasterization (this term comes from television, and the scans that make up a television picture are often called raster). Because bitmap images consist of a large number of rows and columns, the sharpest lines in the image occur closer to the x or y axis. (The outlets near a single row in the vertical direction and the outlets near a single row in the horizontal direction)

When you look closely at lines or curves that are at an angle to the x or y axis, you will notice aliasing because the program simply inserts a predetermined image path by closing or opening a small square in the grid. In other words, the program cannot sketch a smooth curved edge.

The resolution of a bitmap image is determined by the size of the small squares. The smaller the square, the clearer and clearer the edge of the curve. If you zoom in on a bitmap image, you will visually feel that the degradation of the image is very fast. As the grid is enlarged, the right-angled edges of the small squares will become more pronounced.

Although it is possible to copy a bitmap image with a higher visual resolution, it is necessary to realize that the spatial information of the object in the bitmap image is relative (because the resolution is different, the image size is also not the same) and there is no way to know The absolute size and location of the object in the bitmap image.

This fact has brought great difficulties to industrial printers. For the right engineering drawings, spatial information is crucial.

In fact, the spatial information in digital form is exactly the object studied by engineering drawings, and it is also the difference between other forms of printed matter and engineering drawings. The size and location of objects in ordinary prints are not as important.

For half-tone or four-color printing, software for making bitmap images is very important. Because tonal simulation is the primary task in halftone or four-color printing, and for engineering drawings that require spatial stability, tonality is very insignificant.

This does not mean that bitmaps are not very useful in the production of drawings. In many cases, a rasterized image, such as a scanned logo, can be added to the overall design of an industrial graphic.

At this time, the size and position of the image can be determined based on visual effects, and the operation is simple and time-saving. Bitmap software can be used as a design tool for the initial concept, or as a product's advertising design and other similar graphic products such as product catalogs.
After understanding this information, we can clearly understand the limitations of Photoshop images obtained from customers. We can only get the overall design and color arrangement from it, but we can't judge the actual size. We also cannot import files into any software that can make film and color according to requirements.

Although there are many ways to import bitmap images into those building blocks, in this particular case we have to choose to remake the originals in vector format.

Digital process

So what is a vector image?

Vectors are directional, mathematically represented quantities. Vectors are test units, except for numbers that represent size. The key is the need for digital input. As shown below.

The theory behind vector techniques shows that any path can be represented by a straight line (vector) and an arc (we call it a rotating vector). Therefore, when drawing in vector software, the size and position of the object will be recorded as a mathematical quantity. This information of the painted entity will be saved in a database contained in the drawing file.

Using vector-based software, we can make graphics with the actual size of the object and accurately position each object according to the spatial relationship of each element in the graphic. Because computer information about vector orientation and size is stored accurately in the database, these numbers can be adjusted to measure objects on-demand (enlarge or reduce their size) and maintain their proportional relationship without sacrificing image edge sharpness. degree.

The vector type software defines the size, shape, and position of the object based on the input digital information and accurately completes the production of the image or the graphic. This is very important for industrial drawings, because positioning drawings must be arranged according to a certain characteristic of the corresponding industrial product.

Vector-type software is divided into two types: one is used to create technical legends, such as: Adobe Illustrator, Macromedia Freehand, CorelDRAW, and the other is engineering CAD software. There are many types of software.

Each software has its own unique features that are suitable for making industrial drawings. But no software contains all the features.

There is a certain difference between engineering drawings and ordinary images, because such drawings do not represent an independent entity.

The image of our screening must come from the design of the product. It cannot be based on the graphic design alone. In most cases, engineers or designers describe the most basic information in CAD software. Most customers want engineering drawings to convey production information. CAD software has a strong function in this area. This is why engineers chose it without choosing other vector software.

But when making actual pictures for film color separations, CAD software shows its flaws. Although some people disagree with this statement, the fact is that in today's production environment, any work related to actual product graphics is done by other departments. The department makes drawings based on the product's parameter descriptions and fixed requirements.

If you are a designer, printer, or other process provider in the industry, you are likely to be exposed to AutoCAD. If you are a printer who is specifically responsible for signing contracts with your customers, you will certainly have a lot of trouble with AutoCAD files.

AutoCAD files are generally not used as the final manuscript unless the creators who deal with the needs of the printer are unaware of the screen printing process.

A friend of mine once made architectural drawings on a Mac. He received a DXF file made with AutoCAD. When he opened the file, he thought there was nothing in it. But when the file is closed, all elements of the image are white because almost all AutoCAD users work on a black background. We know that Mac users use a white background. Although this is not a big problem, it will make you feel the different principles of the CAD design software and other graphics production software to complete the task.

Another obvious problem is that it is difficult to export the film directly from AutoCAD unless you have a laser imagesetter. Since the output of film directly from AutoCAD is complicated, many service organizations are reluctant to provide such services.

AutoCAD has been around for many years. There have been 15 versions so far. Each version has its own characteristics. AutoCAD original files have the extension dwg. AutoCAD and other CAD software import files in an interactive format (extension dxf).

However, if the process department is ready to receive AutoCAD files, it is best to install AutoCAD software and request *.dwg files from customers. This is only a suggestion because some design elements cannot be faithfully converted to *.dxf. files. If you absolutely need the *.dxf. file, you can make a hard copy of the *.dwg file for reference.

Source: China and Hong Kong silk screen network